Symbol LS 6000 Series Product Reference Manual page 86

Programming the LS 6000
UPC/EAN Security Level 3
If you have tried Security Level 2, and are still experiencing
misdecodes, select this security level. Be advised, selecting this
option is an extreme measure against misdecoding severely out
of spec bar codes. Selection of this level of security significantly
impairs the decoding ability of the scanner. If this level of
security is necessary, you should try to improve the quality of
your bar codes.
UPC/EAN SECURITY LEVEL 3
5-53